In general, a library apparatus functions as a large capacity external storage. Accordingly, a number of cartridges which accommodate magnetic tapes as storage media, for example, are stored at an accommodation rack in a casing. Then, reading/writing of data is performed against the storage media in each of the cartridges. In addition to the accommodation rack, the library apparatus includes a tape drive unit as a recording/reproducing device and a robot. The tape drive unit performs reading/writing of data against the storage media in the cartridge, while the robot transports the cartridge between the tape drive unit and the accommodation rack.
With the library apparatus, when an access request for a cartridge is received from a host, the robot is moved to the accommodation rack which stores the cartridge. Then, a hand mechanism of the robot is positioned at a cell which accommodates the cartridge. Subsequently, the robot transports the cartridge to the tape drive unit in a state of holding with the hand mechanism and inserts the cartridge into the tape drive unit. A process on the storage medium in the cartridge is performed in the tape drive unit. The cartridge ejected from the tape drive unit after the process is completed is held by the hand mechanism of the robot once more. Then, the cartridge is transported to the accommodation rack by the robot and is accommodated in a predetermined cell.
In the library apparatus, as illustrated in FIG. 15, flags 201 to 204 are respectively arranged at cells 101 to 104 of four corners of a cell group of the accommodation rack 100 so that the robot can position the hand mechanism accurately to each cell of the accommodation rack 100. Here, the flag denotes a mark capable of being read by an optical sensor which is arranged at the hand mechanism. The flag 201 arranged at the cell 101 is a positioning reference flag and the flags 202 to 204 which are respectively arranged at the other three cells 102 to 104 are relative position flags.
Here, the accommodation rack 100 illustrated in FIG. 15 is constituted with the cell group of cells 100a which are pieces of five multiplied by six by connecting five sets of subunits in the lateral direction (i.e., the horizontal direction), the subunit being arranged by layering and integrating six cells 100a in the longitudinal direction (i.e., the vertical direction). The cells at the four corners among the cells 100a which constitute the cell group are specified by numerals 101 to 104.
Upon initialization of the apparatus at the time of powering etc., first, respective position data and image data of each of the flags 201 to 204 are obtained by positioning the robot (i.e., the hand mechanism) to the flags 201 to 204. Based on the position data and the image data of four positions which are obtained as mentioned above, a deviation amount of the actual position from the design position of each cell is calculated in the vertical direction and the horizontal direction. Then, when the robot is positioned to each cell, the positioning control of the robot against the cell is performed by utilizing the calculated deviation amount as correction data.
Specifically, the position of the whole accommodation rack is recognized by reading the four flags 201 to 204. Accordingly, the frontage of the cell group is perceived as a surface. Subsequently, the frontage of the cell group is meshed in accordance with the number of the cells. Then, based on the mesh, the center coordinates of the frontage of each cell 100a is obtained as the position of each cell 100a. The position correction of each cell 100a at the abovementioned initialization of the apparatus is effective in a case that cell arrangement of the cell group of the entire surface of the accommodation rack 100 is uniform and all of the cells 100a are deformed evenly against the deformation of the casing of the library apparatus.
Here, in the library apparatus which has a number of cells, a cell group at a surface of an accommodation rack is constituted with a plurality of subunits which are formed to be divided. As mentioned above, in the example of FIG. 15, the subunit is formed to be integrated by superimposing six pieces of cells 100a in the longitudinal direction. Then, the accommodation rack 100 is formed by connecting five sets of subunits in the lateral direction. Accordingly, there is a case that an attaching position of only one subunit is deviated from other subunits depending on assembling accuracy of each subunit itself or assembling accuracy of mutual connecting of the subunits or due to deformation of the casing by receiving some impact etc. during transportation of the library apparatus. In FIG. 15, the attaching position of only a center subunit A among the five subunits which are connected in the lateral direction is slightly deviated from other subunits in the right lateral direction.
In a case that the abovementioned apparatus initialization is performed in a state that only the subunit A is deviated from the other subunits, the positioning control of the robot can be accurately performed against the cells of subunits other than the subunit A (for example, the cell of (1)). Therefore, inserting and extracting of a cartridge can be performed without a problem against the cells of the subunits other than the subunit A. However, when the robot is positioned at the cell which belongs to the subunit A (for example, the cell of (2)), the positioning control cannot be accurately performed with the correction data obtained by the above-mentioned apparatus initialization since the deviation amount of only the subunit A is not even in the lateral direction. In particular, when the deviation amount exceeds the allowance error range of the positioning of the robot, there arises a case that the robot cannot perform the inserting and extracting of the cartridge against the cell of the subunit A.
In a case that the inserting and extracting of the cartridge against the cell cannot be performed, normally, the robot is operated with retry control for searching a position at which the inserting and extracting of the cartridge can be performed while shifting the position of the hand mechanism slightly in the vertical direction and the horizontal direction. Since such retry control accompanies the inserting and extracting of the cartridge by the hand mechanism, there is a risk that a mechanical part of the cell or the hand mechanism of the robot is interfered and broken. At the worst, there is a risk that the library apparatus becomes incapable of being operated and system-down is caused.